1. Field of the Technology
The invention relates to the communications technology, and in particular, to a method and devices for providing wetting current to subscriber lines.
2. Background of the Invention
In communication networks, multiple metallic lines are needed to connect an exchange or an access network to User Equipment (UE). These connections may include connections between a device and a distribution frame, between an internal-line bar and an external-line bar of distribution frame, between the external-line bar of the distribution frame and a main cable, between the main cable and a cross-connection box, and between a junction box and UE. In such connections, multiple wire splices exist. Since these wire splices are generally exposed in the air, wire splices are inclined to be oxidized with the extension of service time. Severe Oxidation of wire splices may degrade the quality of connection of copper lines and result in degradation of transmission of signals.
In terms of the above problem, a general solution in the field is to continually or intermittently provide a certain Direct Current (DC) loop current, also called wetting current, on lines to protect the wire splices of the lines.
The early Asymmetric Digital Subscriber Line (ADSL) and Very high speed Digital Subscriber Line 2(VDSL2) usually work with the traditional telephone service. With reference to FIG. 1, no wetting current is needed since DC feeding current provided by the traditional voice network device may serve as wetting current. The DC feeding current is provided on copper lines to UE by the general telephone service. When the phone is off-hook, the current may pass copper lines and prevent the wire splices from oxidation, thus no wetting current is needed.
Along with development of network technologies, traditional voice services are provided by ADSL/VDSL2 broadband networks or wireless networks, and many applications in pure broadband mode emerge gradually. In these networks, the traditional telephone service working in DC mode no longer exists. The traditional network device for providing voices may quit services gradually, and the new broadband network device may no longer provide or may provide few traditional voice services. As a result of such a change, operators can lower the fixed asset investment on traditional voice network interfaces, and meanwhile reduce the associated maintenance and operation cost with the decrease of devices. Therefore, due to the absence of traditional voice line cards, no device may provide the DC loop current on lines. In this case, it is urgent to provide wetting current on network devices to meet the requirement of preventing wire splices from oxidation.
However, since the current Single-pair High-bit-rate Digital Subscriber Line (SHDSL) technique works with no DC and uses the 0-4 k band of general voices, a network device is needed to provide DC current to guarantee the reliable connection of wire splices. The wetting current function has been integrated in many network devices for the SHDSL interface. Such a wetting current is generally implemented by building a wetting current circuit in an SHDSL link card.
In order to provide the wetting current for preventing copper lines from rustiness, one solution is to preset a wetting current circuit in a broadband link card of a network device, as shown in FIG. 2. When the traditional network device that provides voices stops working, the wetting current circuit is activated to provide a wetting current on line loops. In this solution, In order to construct the loop of wetting current, the UE-side device is required to be modified properly to construct a wetting current loop.
When using the above solution, the broadband link card in the existing broadband device is first required to be replaced by a new one that has ability to support the function of presetting the wetting current circuit. For building new devices, this solution complicates the construction of a broadband link card and increases cost. In addition, the function of supporting wetting current circuit needs developing for various broadband line cards including SHDSL, ADSL and VDSL, thus leading to relatively higher cost. Furthermore, increased power consumption of the system caused by providing wetting current function is relatively high.
In order to provide the wetting current for preventing copper lines from rustiness, another solution is to provide a wetting current circuit for each line interface in a splitter card to replace the feeding of traditional voice devices. As shown in FIG. 3, when the traditional voice line card of plain old telephone service (POTS) stops working, the corresponding wetting current circuit may be connected to the line via a built-in switch to provide the wetting current to the line.
However, the above solution is unsatisfactory in that, this solution is more applicable to new devices, while the original splitter cards in existing broadband devices have to be replaced by the card that supports wetting current function, which limits the application of this solution. Furthermore, the power consumption of system for providing wetting current is relatively high. 0.3 w of power consumption are needed in normal condition of each line based on an average of 6 mA per line, which will bring such problems as heat dissipation to the network device with large capacity and high density.